Sharif Digital Repository

Among the various types of black holes, dilatonic black holes can be mentioned which are in the center point of view at their extremality. In this study, we pay attention to these answers and their fields and the way they behave variously, especially when the coupling constant α is between 0and1. For doing so, in chapter one we attempt to study one of the simplest answers in General Relativity (Schwarzschild) and some beginning contexts. Then in chapter two, we try another answer (Reissner Nordstrom) which contains non-Extremal and Extremal states. In chapter three we introduce the concept of the higher theories. Chapter four is a hint about hawking radiation. And finally in chapter five, we... 

Discovery of the Higgs boson which is pivotal to the Standard Model of elementary particles, at the LHC in the 2012, was a major breakthrough in the particle physics. Despite all theoretical elegance and all experimental confirmations, undoubtedly Standard Model is not the end of the way of Particle Physics. Standard Model defects and unanswered questions in the particle physics have led physicists to the Beyond the Standard Model theories. Among extensions of the Standard Model, the Minimal Supersymmetric Standard Model (MSSM), due to its theoretical appeals and experimental challenges has engaged people in research in this field in all around the globe. In this thesis we have studied the... 

In this thesis we first discuss the final fate of a spherical symmetric distribution of matter which has undergone a gravitational collapse, by reviewing some classical collapse models. Our emphasis will be on the visibility of singularity after it forms. Then we will mention some general aspects of quantum field theories in curved space-time and after that we investigate the quantum background effects on the evolution of a spherical symmetric and homogeneous distribution of dust. In fact by calculating the quantum corrections—due to massless scalar fields which are arbitrarily coupled to the background geometry— on the geometry of collapsing sphere, one can obtain the quantum corrected... 

In this thesis we have used the low energy effective action of the string theory to find an asymptotic Anti-de sitter metric with a non-vanishing H field. Then we have used the AdS/CFT correspondence to study the effects of the added Kalb_Ramond field on two calculations in the boundary theory. The first one was the calculation of the drag force exerted on a moving quark in the quark-gluon plasma. In the second calculation we observed the effect of the added field on the confinement-de confinement phase transition  

The purpose of this thesis is to study the behaviour of open strings between two parallel D-Branes in the presence of a background Kalb-Ramond field linearly varying perpendicular to D-Branes. In an attempt to solve the nonlinear equations of motion we found two sets of nontrivial solutions: String wrapped around a cylinder with constant velocity along its axis and a rotating string with oscillatory radius perpendicular to D-Branes, such that knots are shaped. Considering the boundary conditions, the constraints on these solutions, conserved currents and Mass are found. In particular calculated linear momentum for the first set of solutions suggests the possibility of using this setup as an... 

Since 1980’s, String Theory is considered as one of the main candidates for the unified theory of nature. One of the important features of this theory, is describing the Gravity as a renormalizable quantum theory. An interesting and important problem is the interaction of the string with classical fields in spacetime such as gravity. The conclusions which can be deduced may be very different from the standard results in case of absence of these classical fields.On the other side, for giving a solution to one of the unsolved problems in standard model of particle physics, the hierarchy problem, Lisa Randall and Raman Sundrum in1999, suggested a model which assumes that spacetime may has... 

We study a speci?c class of black holes which are called extremal. By de?ning extremality asdouble-horizon condition and imposing ?niteness assumption, we show that the dynamics of ?eldsat the horizon decouples from the rest of space. This decoupling occurs by vanishing all radialderivatives. We show this decoupling for the extremal black holes in the theories of gravity correctedby f(R)terms.We also show that these two above conditions leads to AdS × S1 near horizon geometry2of rotating black holes. This geometry which preserve SO(2, 1) × U(1) isometry group, is recentlyused in improving the entropy function method. Finally we show that decoupled equations of horizon can be derived from a... 

To investigate many interesting and rare physics processes at the Large Hadron Collider, we need much more data. The High Luminosity LHC (HL-LHC) is a foreseen upgrade for LHC to increase its luminosity and get ten times more data until the end of HL-LHC.Without any intervention, The CMS ECAL will face many challenges in HL-LHC. The end-caps must be fully replaced, and the electronic structure of the barrels will be modified. This thesis addresses the R&D studies of both sections.For the barrels, a test beam experiment has been performed on a prototype 5x5 matrix of legacy PbWO4 crystals with the new Very Front End (VFE) boards and the data has been analyzed.For endcaps, a 3x5 martix of... 

Langlands Program or Langlands Correspondence is a unified theme for many important results of number theory, which proposed by Robert Langlands in the late 1960's. The aim of this program is to relate intricate problems of arithmetic to analysis and use powerful methods of analysis to investigate these problems. One of the main aspects of this duality is the appearance of two dual groups in two sides of it that can be obtained from one another. In the 1980's, by the work of many mathematicians, it turns out that a geometrical version of this duality can be formulated. In the last ten years, a categorical version of duality is worked out. On the other hand, by the work of physicist like... 

In 2004 Ooguri, Strominger, and Vafa could write the partition function of 4D N=2 extremal black holes in type IIA superstring theory as the square of the absolute value of the partition function of type A closed topological string theory, which had already been introduced by Edward Witten in 1990. In this study, T and S dualities were applied to the original conjecture of Ooguri, Strominger, and Vafa. By using T duality, we have verified that the conjecture holds for 4D N=2 extremal black holes of type IIB superstring theory to the one loop order in string coupling. In other words, one can write the partition function of these kinds of black holes as the square of the absolute value of... 

Inthisthesiswe willuse curved space-time quantum mechanicsto solveDirac equationin the background of dilaton black hole. Graybodyfactors and Hawking radiation and evaporation rates of charged massive spin particles in the background of dilaton black holes is obtained. The results are analyzed and the lifetime of dilaton black hole in terms of different dilaton coupling constants is studied  

In this thesis by studying the extreme physical conditions near black hole horizons and singularity, we attack intriguing problems in the exciting era of quantum black holes and gravitational wave astronomy. We considered the backreaction of the energy due to quantum fluctuations of the background fields for a Schwarzschild black hole, in semi-classical gravity. We have shown that it results in modification of the horizon and also formation of an inner horizon. The process of the collapse of a thin shell stops before formation of the singularity. After the collapse stops the reverse process takes place. We also demonstrate the existence of a cold remnant for the black hole. We generalized... 

The Large Hadron Collidor (LHC) will increase its luminosity to more than 10e35 cm-2 s-1. The large amount of data rates will provide enough datasets needed to probe rare Higgs processes, study the scattering of longitudinally polarized W bosons and physics beyond the standard model(BSM). In the upgraded version of the LHC, called High Luminosity LHC (HL-LHC), the number of simultaneous interactions per bunch crossing, aka pile-up, increases to 140-200. The large number of pile increases the possibility of confusion in distinguishing vertexes of interest due to the contamination from non-interesting vertexes. One of the methods to mitigate the pile-up, complementary to the precision tracking... 

Among the proposals for new physics, Supersymmetry is the most popular to gradually appear at a yet unreached center-of-mass energy at the Large Hadron Collider (LHC). However, that doesn’t seem very likely. This thesis represents a search for any evidence of a minimal supergravity inspired scenario (mSUGRA) of R-parity conserving supersymmetry at the Compact Muon Solenoid (CMS) experiment. The analysis employs an event topology , which consists primarily of opposite-sign di-leptons accompanied by hadronic jets and missing transverse energy. The search utilizes data produced by the proton-proton collision of the LHC at a center-of-mass energy p s = 7 TeV and recorded by the CMS detector in... 

In this thesis, we show that conformal Chern–Simons gravity in three dimensions has various holographic descriptions. They depend on the boundary conditions on the conformal equivalence class and the Weyl factor. The boundary conditions on the Weyl factor of the metric lead to three physically distinct scenarios: I. trivial Weyl factor, II. non-trivial but fixed Weyl factor and III. free Weyl factor. The metric is not necessarily asymptotically AdS in cases II and III, but nevertheless a dual CFT appears to emerge. We focus on a particular case III where an affine U(1) algebra related to holomorphic Weyl rescalings shifts one of the central charges by 1. The Weyl factor then behaves as a... 

One of the approaches to study the plasma phase of quantum chromodynamics is to investigate the motion of probes in the quark-gluon plasma. In the case of a moving heavy quark, the medium affects the quark by exerting a drag force on it. Since we finally detect hadron jets in detectors, the goal is to compute the darg force formula in a form compatible with the espectrum of final hadrons. On the other hand due to strong coupling, perturbative methods fail in the medium. So a nonperturbative method is needed. We use gauge gravity duality and compute the drag force exerted on a heavy quark in the hydrodynamic regime, up to first order in derivative expansion  

According to the AdS/CFT correspondance,Gravity in an asymptotically AdS spacetimes has a conformal field theory dual. One of the perplexing concepts in theoretical physics is obtaining a comprehensive understanding of holography. To this end, it is of interest to explore whether holography exists beyond the known example of the AdS/CFT correspondence and for spacetimes other than the AdS. asymptotically flat spacetimes are of great theoretical importance.A correspondence has recentlay been proposed,which is between asymptotically flat spacetimes and a field theory with Galilean conformal symmerty and it is known as BMS/GCA correspondance.In this thsis,we have reviewed this correspondence... 

In the present thesis, two subjects have been studied. In the first one we introduce the theory of holographic superconductors. Using the gauge/gravity correspondence, many of the features of perconductors will be explored. Analyzing the five-dimensional AdS gravity coupled to a gauge field and a charged scalar field, we can recognize the system undergoes a superconductor/insulator transition at zero temperature and critical chemical potential.We consider the backreaction effects to construct the complete phase diagram for the system. For a determined chemical potential there are typically two phase transitions as the temperature is lowered.we also discuss the zero temperature limit of a... 

Models wih extra dimensions have been among the most important models built for solving the problems of the standard model. In the standard model, Higgs mechanism is used to ex-plain electroweak symmetry breaking. One of the theoretical problems of the standard model,the hierchy problem, is about the Higgs mass being unnaturally small and models with extra dimensions have provided solutions to solve the problem. Moreover, extra dimensions pro-vide tools using which several models have been developed to explain electroweak symmetry breaking. In this thesis, acher reviewing the electroweak symmetry breaking sector of the stan-dard model, and the hierarchy problem, some models of electroweak... 

Entanglement is an immediate consequence of quantum mechanical pos- tulates and is thus an indispensable part of studying quantum systems. A very useful quantity which can appropriately quantify entanglement between the degrees of freedom of a composite quantum system is En- tanglement Entropy (EE).
Over the last few years, this subject has attracted a lot of interest both in QFT and in the context of holography. On the one hand, an intu- itive geometrical Holographic model for entanglement entropy has been proposed in the context of gauge/gravity duality, and on the other, var- ious issues concerning entanglement have been explored, e.g. in quan- tum computation, quantum information...